1. Field of the Invention
The present invention relates to a droplet ejecting apparatus for stably and accurately ejecting micro droplets. More specifically, the present invention relates to a droplet ejecting apparatus, which can be promptly operated at an arbitrary moment when said droplet ejecting apparatus is operated, in which case the amount of droplets actually ejected is quantitatively measured, and control is performed, based on the information obtained by the quantitative measurement.
2. Description of the Related Art
Micro droplet ejecting means play an essential role in the fields of biotechnology as well as in the fields of manufacturing chemicals, foods, etc, since the stability regarding the amount of ejected droplets and the accuracy regarding the position thereof directly relates to the quality and the producibility of the products manufactured using the droplet ejecting apparatus.
Generally, the amount of droplets is normally determined only by the droplet ejecting means itself. However, there is no means for determining the final positions at which the ejected droplets arrive. At present, the products produced from ejected droplets are inspected in an initial test in terms of the quality and/or byproducts produced from the ejected droplets by using certain detection means. On the basis of the results obtained in these investigations, the droplet ejecting means is controlled. As a result, a relatively long inspection period is necessary in periodical inspections of the ejected goods or articles, and therefore there is a problem in that the productivity is reduced. If the amount of a droplet can be evaluated in real time without delay for each ejection, the inspection can be frequently carried out without any reduction in the productivity, so that in an early stage either a bad condition can be ascertained or variations in quality can be suppressed, thereby allowing a high quality to be maintained. Such requirements have been previously described.
For instance, a method for uniformly mixing materials and a mixing apparatus have been proposed in Japanese Unexamined Patent Application Publication No. 11-262644. In the specification, it is pointed out that a treatment of mixing micro materials and reacting them with each other is required for research in the field of biotechnology, and in order to satisfy these requirements, two or more piezoelectric control type droplet ejecting means are employed. By colliding micro droplets ejected from different droplet ejecting means with each other, these droplets can be uniformly mixed, thereby enabling different materials to be uniformly reacted with each other, thus allowing uniform reaction products to be obtained.
In such a method for uniformly mixing materials as well as in such a mixing apparatus, the rate of non-collision is determined by collecting uncollided droplets, thereby allowing the collision rate to be increased by correcting the ejection direction of the materials on the basis of the thus determined rate of non-collision via a feedback system.
Moreover, the origin of the instability in the ejection, for instance, the deflection of a droplet flight direction, the variation in both the purity and the reaction of the droplets, the variation in the reaction speed due to variations in temperature and/or variations in both the viscosity and specific gravity of the liquid in a fluid channel, must be investigated in advance, and such instability should preferably be suppressed, based on the results obtained from the investigation.
In these methods, the state of an apparatus was controlled by determining the conditions of operation indirectly relating to the ejection of droplets.
Furthermore, for instance, in Japanese Unexamined Patent Application Publication No. 8-201265, a viscosity measuring apparatus and a method for determining fluid characteristics have been proposed. In this specification, it is emphasized that it is important to measure the viscosity of a fluid in order to ensure the quality of products and/or to control the process for manufacturing the products, where the products are in the form of a fluid, e.g., a chemical, food, lubricant, car wax or the like, and for this reason the viscosity of the fluid is determined, based on the change in the specific electrical constant of an oscillating element made of a piezoelectric material, where the oscillating element is oscillated in the fluid and is subjected to a mechanical resistance resulting from the viscosity of the fluid.
When an anomaly is found in the specific electrical constant of the piezoelectric element, the ejection of droplets is set to cease and then a recovery treatment is performed.
In this method, there is an advantage in that the piezoelectric element can be used not only as an actuator but also as a sensor. However, the piezoelectric element is used exclusively to monitor the characteristics, such as the viscosity, of the fluid stored in a cavity or the like before the ejection, and not to monitor the characteristics of the droplets after ejection.
Moreover, in order to determine the amount of liquid ejected, an electronic force balance is conventionally used to measure the accumulated mass of ejected droplets within the measurement range of the balance, and the mass of one droplet is determined by dividing the accumulated mass by the number of droplets. This method is also unsuitable for controlling the stability in the amount of ejection for a droplet.
Moreover, the present applicant has proposed a micropipette and a separate injecting apparatus in Japanese Patent Application No. 11-301626. In the specification, it is emphasized that, in the production of a DNA chip for analyzing gene structure, it is important to suppress variations in the volume and the shape of individual micro droplets and to preserve the distance between the micro spots at a fixed value. It is described that the micropipette comprises both a main body including a sample supplying opening, a cavity for storing the sample and a sample discharging opening, and a piezoelectric element mounted on the outer surface of the main body at the position corresponding to the cavity, and it is also described that a certain amount of the sample in the cavity can be ejected from the sample ejecting opening with the aid of a change in volume of the cavity by activating the piezoelectric element, thereby enabling micro spots such as DNA chips to be formed very accurately and rapidly.
In this proposal, the cavity is filled in advance with a substitution solution, such as buffer solution or physiological saline solution, and then a sample is supplied into the cavity from the sample supplying opening, by substituting the substitution solution therewith in a laminar flow. After that, the piezoelectric element is activated. In this case, the completion of the substitution in the cavity using the laminar flow is preferably determined not by the volume and moving speed of the sample, but by the change in fluid characteristics in the cavity, in which case the piezoelectric element is activated by applying a voltage thereto and the change in the specific electrical constant in the oscillation of the piezoelectric element is sensed.
In order to more accurately determine the completion of the laminar flow substitution, it is desirable that the change in the characteristics, not of the liquid in the cavity, but of the droplets actually ejected therefrom be measured, if possible. From this viewpoint, the present applicant tried to further modify the droplet ejecting apparatus, and made certain discoveries to reach the present invention, after many investigations.
As described above, it is necessary to maintain the stability in the amount of droplets ejected from a micro droplet ejecting means and the accuracy in sensing the arrival position of the droplets, e.g., in the formation of DNA chips which are necessary for the treatment of mixing and reaction and for analyzing gene structure in biotechnology, or in the formation of micro spots which are necessary for producing protein chips which are used to analyze proteins and the interactions of proteins on the basis of the information, or in the synthesis of liquids in the process of manufacturing chemicals, foods, oil products, etc. In this case, it is desired that the ejection of micro droplets is carried out, not by using a method for analyzing the indirect information resulting from the ejection, but by using a method for directly measuring in real time the ejected droplets themselves.
Accordingly, it is an object of the present invention to provide a droplet ejecting apparatus which permits secure sensing of variations in the amount of each droplet ejected, the occurrence of ejection, and the deviation of the arrival position to which the droplet is ejected by accurately determining in real time the amount of droplets actually ejected from the micro droplet ejecting means.
It is another object of the present invention to provide a droplet ejecting apparatus which permits control of the amount of droplets ejected from droplet ejecting means and the arrival position of the ejected droplets, by feeding back information on the amount of the droplets to the droplet ejecting means, so that the mixture of the droplets can be homogenized.
It is another object of the present invention to provide a droplet ejecting apparatus which permits possible problems in the droplet ejecting means to be detected at an early stage and the droplets to be stably ejected in a predetermined amount based on the results obtained regarding the arrival position of the ejected droplets.
It is another object of the present invention to provide a droplet ejecting apparatus, which can provide products having high productivity, high quality and good reliability in the field of biotechnology, as well as in the fields of manufacturing chemicals, foods, oil products, etc.
The applicants investigated the method for detecting the failure of droplet ejection, and the method for quantitatively evaluating the droplet, and chose the measurement of the mass of the droplet as a quantitative measuring method, since the results obtained by the method were not influenced by the change in volume of a droplet ejected due to the change in the characteristics of the droplet, e.g., the viscosity, nor by the intentionally changed composition of the droplet. In the method, using both the droplet ejecting means to which an electrical signal can be supplied and the droplet quantity evaluation means, which allows the mass of a micro droplet to be measured and the measurement result to be supplied as an electrical signal, the state of ejection can be ascertained by measuring the mass of a droplet ejected during the operation of the droplet ejecting apparatus. By feeding back the information thus obtained to the droplet ejecting means, the ejection of the droplets can be controlled, so that a predetermined amount of the droplets can be securely ejected to a predetermined position. Hence, the observation of the amount of the ejected droplets and the arrival position thereof is feasible with the droplet ejecting apparatus itself, so that it is possible to automatically correct a possible ejection failure, for instance, an undesirable change in the amount of ejected droplets.
In accordance with the present invention, the following droplet ejecting apparatus is provided in order to attain the above objects.
A droplet ejecting apparatus for ejecting micro droplets comprises at least one droplet quantity evaluation means, wherein the mass of a droplet ejected onto an article is measured, and a measurement signal is generated based on the measurement result; feedback control means, wherein the measurement signal is compared with a respective reference value and then a control signal is generated based on the result of the comparison; and at least one droplet ejecting means for adjusting the amount of ejection for the droplet on the basis of the control signal.
In accordance with the present invention, it is preferable that the droplet ejecting means comprises a micropipette including a cavity for storing a liquid, and a piezoelectric element for changing the volume of the cavity.
Moreover, it is preferable that the droplet quantity evaluation means comprises a measuring member for measuring the change in resonance frequency as a result of receiving the droplet and for supplying the measurement result as an electrical signal, a processing member for determining the mass of the droplet by executing a predetermined calculation on the basis of the supplied electrical signal and for supplying the measurement signal, wherein the measuring member comprises at least a resonance member for providing a change in the resonance frequency in response to the mass of the droplet received by the measuring member, and a frequency measuring member for measuring the change in the resonance frequency, and wherein the resonance member comprises a substrate, a diaphragm for receiving the ejected droplet, a sensing plate including the piezoelectric element for sensing the resonance frequency in the resonance member and a connection plate for connecting the diaphragm and the substrate.
In the droplet ejecting apparatus according to the invention, it is preferable that the mass of the ejected droplet received by one surface or both surfaces of said diaphragm is measured. Moreover, it is preferable that the droplet quantity evaluation means and/or the droplet ejecting means is moved in such a manner that the droplet quantity evaluation means can receive the droplets, and then the mass of said droplet is measured.
In accordance with the present invention, moreover, it is preferable that the droplet quantity evaluation means evaluates the resonance frequencies in the resonance member before and after the droplet is received, and determines the mass of the droplet ejected from the droplet ejecting means on the basis of the evaluated change in the resonance frequency.
It is preferable that the resonance frequency corresponds to the resonance frequency in the oscillation mode consisting mainly of the xcexd mode oscillation, where the diaphragm linearly reciprocates in the direction parallel to the plane of said diaphragm and perpendicular to the vertical axis vertically passing through a joined plane of the connection plate and the substrate.
In the droplet ejecting apparatus according to the invention, it is preferable that for the maximum size b of the diaphragm in the direction of the vertical axis perpendicularly passing through the joined plane of the connection plate and the substrate and for the maximum size a of the diaphragm in the direction parallel to the flat plane and perpendicular to the vertical axis, the ratio of the sizes satisfies the following relation:
0.7 less than a/b less than 5.
Moreover, it is preferable that for the thickness t (cm) of the diaphragm, the density dc (g/cm3) of the diaphragm, the volume V (cm3) of a droplet and the density dr (g/cm3) of the droplet, and the area S (cm2) of the diaphragm are set within a range at which the following relation is satisfied:
2.5xc3x9710xe2x88x925+(1.5xc3x97V)2/3xc3x97xcfx801/3 less than S less than Vxc3x97drxc3x97106/(txc3x97dc).
In the case where the resonance frequency used for measurement is the same as a resonance frequency in the oscillation mode consisting mainly of the xcexd mode oscillation, it is preferable that the droplet quantity evaluation means and/or the droplet ejecting means is moved in such a manner that the droplet quantity evaluation means receives the droplet in the main oscillation direction of the diaphragm.
Except for the oscillation mode consisting mainly of the xcexd mode oscillation, it is preferable that the resonance frequency is the same as a resonance frequency in the oscillation mode of the rotation-around-axis oscillation where the diaphragm reciprocates in a rotary oscillation around a vertical axis passing through the joined plane of the connection plate and the substrate. Moreover, it also is preferable that the resonance frequency is the same as a resonance frequency in the oscillation mode of the rotation-in-plane oscillation where the diaphragm reciprocates in a rotary oscillation in a plane containing the diaphragm in such a manner that the center of rotation is situated at least within the diaphragm.
In accordance with the present invention, it is preferable that the direction of ejection in the droplet ejecting means is controlled on the basis of the difference in the sensitivity in the plane of the diaphragm in accordance with the distance from the center of rotation in the diaphragm.
Moreover, it is preferable that the droplet quantity evaluation means has a measurable range of mass greater than the mass of a droplet ejected, and wherein the mass of droplets are can be determined by repeatedly measuring the mass of each drop with the same droplet quantity evaluation means.
In accordance with the present invention, it is preferable that the droplet quantity evaluation can be promptly operated at an arbitrary moment when the droplet ejecting apparatus is operated.
The present invention demonstrates a droplet ejecting apparatus comprises one or more droplet ejecting means to which an electrical signal can be supplied; one or more means for evaluating the quantity of droplet, said means performing the measurement of a micro droplet, and from said means an output being electrically supplied; and a feedback control means to which the electrical signals can be supplied and output, and in said control means various calculations being performed, based on the measurement results regarding the change in the mass of a droplet.
In the present invention, droplets are received by the droplet quantity evaluation, either while moving the droplet ejecting means, or while moving the droplet quantity evaluation on the flight trajectories of the droplets ejected from the droplet ejecting means. Under such a condition, the mass of the ejected droplet is continuously monitored and the monitored results are transferred to the droplet ejecting means, thereby enabling a predetermined amount of droplets to be securely ejected to a predetermined position.
In the present invention, the control of the droplet ejecting means is carried out, not by monitoring the property of droplets before ejection and/or determining the conditions of products indirectly relating to the ejection of droplets, but by measuring the mass of the ejected droplets in real time during the operation period of the droplet ejecting apparatus. With this control, the quantity of each droplet can be evaluated more accurately and a possible failure of ejection can be suppressed, thereby enabling both the quality of the manufactured products and the productivity to be enhanced. The droplet ejecting apparatus according to the invention can be used as a calibration system before or after the operation thereof. However, it is preferable that the apparatus is used to measure in real time the quantity of droplet and to securely avoid a possible ejection failure.
Moreover, the range of mass measurable with the droplet ejecting means in the droplet ejecting apparatus can be set to be greater than the mass of a droplet to be measured. With this structural arrangement, the droplet quantity evaluation means can receive the droplets repeatedly ejected from the droplet ejecting means, and can continuously measure the mass of droplets received or deposited thereon. The mass of each droplet can be determined by the differentiation of the measured results for the ejected droplets.